Jump to content

Tandy 1000A Capacitor Replacement Guide

From RetroTechCollection
Tandy 1000A main logic board component layout (Service Supplement p. 23)
The 1000A main board layout. C110, C110A and C111 are near the bottom right, beside the expansion slots; C6 and C10 are at the top, near the speaker connector J1 and U7.

The Tandy 1000A main logic board has fourteen electrolytic capacitors, all axial, and their values are in Tandy's 1985 service supplement for the 1000A.[1] The power supply is the original Tandy 1000's 54 W unit, Tandy part 8790070, so its capacitors are listed on Tandy 1000 Capacitor Replacement Guide.[2] See Capacitor Failure Symptoms for the signs of a failing part.

[3]

Main logic board

[edit | edit source]

The board is the Main Logic T1000 PC board, revision B, Tandy part 8709604B.[1]

1000A main board electrolytic capacitors (parts list p. 16)
Ref Capacitance Rating Type as listed Tandy part no.
C5, C49, C72, C79, C80, C110, C110A 22 µF 16 V Axial, ±20% 8316221
C6, C112 100 µF 16 V Axial, non-polarised 8317101
C10, C25, C106, C109, C111 10 µF 16 V Axial electrolytic 8316101

Watch the suffixes: C10A is a 100 pF ceramic and C49A a 0.1 µF part, not electrolytics, while C110A is one of the 22 µF positions.[1] The list has no tantalum capacitors. The rest of the board is 0.1 µF axial decoupling capacitors, ceramic timing and filter parts, a 0.022 µF polyester capacitor (C39) and a 0.47 µF part (C107).[1]

C6 and C112 are non-polarised, so replace them with bipolar parts of the same value, not ordinary electrolytics. On the schematic, C6 couples the LM386 amplifier (U7) to the speaker and C112 sits in the audio line on the same sheet.[4]

The references and values differ from the original 1000's board, so use the original's list only for an original board.

Power supply

[edit | edit source]

The 1000A assembly list names the 54 W supply 8790070, the unit covered by the original 1000's service manual.[2] Its electrolytics (C4 on the primary side, C11 to C20 on the secondary side), the notes on two doubtful lines in Tandy's list and the test after replacement are on Tandy 1000 Capacitor Replacement Guide.

Keyboard and floppy drive

[edit | edit source]

The supplement has no keyboard or drive parts lists. The 1000A assembly list gives the drive as Tandy part 8790127 without naming the maker.[2] The original 1000's keyboard capacitors and the TEAC FD-54B control board list are on Tandy 1000 Capacitor Replacement Guide; check the make of your own drive before using the TEAC list.

Replacement procedure

[edit | edit source]
  1. Unplug the machine and open it as described in Tandy 1000A General Maintenance.
  2. Photograph the board and note the polarity of every electrolytic before removing it. The axial parts lie flat; the silkscreen shows + marks at polarised parts such as C10, C25 and C110.[5]
  3. Replace one position at a time, matching the capacitance and at least the 16 V rating. Use non-polarised parts at C6 and C112.
  4. Inspect the new joints and the pads around them under a magnifier.
  5. Power the machine and check the supply outputs against the limits on Tandy 1000 General Maintenance, then check the speaker works.
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 1.3 Tandy Corporation, Supplement to the Tandy 1000 Service Manual (Cat. No. 25-1000), covering the Tandy 1000A, 1985, hosted as File:Tandy 1000A Service Manual Supplement (1985).pdf. Section 3, "Parts List", Main Logic Sub Assembly, p. 16.
  2. ↑ 2.0 2.1 2.2 1000A Service Supplement, Section 3, "Parts List", Main Logic Main Assembly, p. 15.
  3. ↑ Radio Shack, Service Manual: Tandy 1000 Computer, catalogue no. 25-1000, 1985, hosted as File:Tandy 1000 Service Manual (25-1000, 1985).pdf. Section 7, "AC Input Circuit", p. 77.
  4. ↑ 1000A Service Supplement, Section 5, "Schematics", audio and joystick sheet.
  5. ↑ 1000A Service Supplement, Section 4, "Component Layout", p. 23.


Retrieved from "https://retrotechwiki.com/index.php?title=Tandy_1000A_Capacitor_Replacement_Guide&oldid=29504"